Color cathode ray tube

ABSTRACT

Disclosed is a color cathode ray tube in which an inner curvature radius is designed as 0.3≦(Rx3/Rxc)≦0.75. According to this, a structural intensity of a mask is obtained thus to increase a drop characteristic and to effectively prevent a partial doming.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a color cathode ray tube, andmore particularly, to a color cathode ray tube capable of obtaining astructural intensity of a mask corresponding to a panel, decreasing apartial doming, and increasing a drop characteristic by setting acurvature of the panel to be greater from a center portion of the paneltowards a peripheral portion thereof.

[0003] 2. Description of the Related Art

[0004] Generally, a color cathode ray tube is for implementing images,and is divided into a curved type cathode ray tube and a flat typecathode ray tube according to an appearance of a panel.

[0005] The curved type cathode ray tube has several problems such as animage distortion, eyes fatigue due to light reflection, and etc. thus tohave decreasing demands, whereas the flat type cathode ray tube hasadvantages in that images are not distorted, reflection for externallight is minimized, and maximization of a visual region can beimplemented thus to have increasing demands.

[0006]FIG. 1 is a longitudinal section view showing a color cathode raytube in accordance with the conventional art.

[0007] As shown, the conventional color cathode ray tube comprises apanel 1 having a fluorescent surface la, a mask 2 for selecting colorsof electron beams incident from an inner side of the panel 1, a funnel 3coupled to a rear surface of the panel 1 for maintaining inside of thecathode ray tube as a vacuum state, an electron gun 5 mounted in a neckportion 4 of the funnel 3 for emitting electron beams, and a deflectionyoke 6 for surrounding outside of the funnel 3 and deflecting electronbeams.

[0008] In the conventional color cathode ray tube, when image signalsare inputted to the electron gun 5, the electron gun 5 emits electronbeams and the emitted electron beams are accelerated and focused towardsthe panel 1 according to voltages applied from each electrode of theelectron gun 5.

[0009] At this time, the electron beams are deflected by the deflectionyoke 6 thus to pass slots formed at the mask 2, and thereby colors ofthe electron beams are selected. Then, the electron beams collide withthe fluorescent surface la inside the panel 1 thus to make eachfluorescent surface 1 a emit light, thereby reproducing images.

[0010] In the conventional color cathode ray tube, a method for reducinga center thickness of a panel or a method for flattening an innersurface of a panel were used in order to make the cathode ray tube lightand to reduce a cost.

[0011] However, in the method for reducing a center thickness of apanel, when the center thickness of a panel becomes thinner than acurrent standard of 10.5 mm, x-ray emission amount is increased thus tohave a limitation.

[0012] Also, in the method for flattening an inner surface of a panel,the inner surface of a panel becomes gradually flat and thereby acurvature of a mask becomes gradually flat, thereby decreasing astructural intensity of a mask and thus deteriorating a drop quality (adrop characteristic). Also, when the panel mask becomes flat, electronbeams which have passed through mask holes do not correctly hit red,green, and blue phosphors of a screen by a thermal expansion of themask, thereby generating a partial doming that a color purity of ascreen is deteriorated.

[0013] To prevent said partial doming, in the conventional art, invarsteel, a low thermal expansion material instead of AK, a high thermalexpansion material was used to fabricate a mask, which was disclosed inJapanese patent 1984-15861.

[0014] In case of using a mask of said invar steel material(hereinafter, invar mask), a thermal expansion of a mask can bedecreased. However, in this case, the cost is high, a mechanicalworkability is very poor thus to have an annealing process temperaturemore than 900° C., and a metallic pattern has to be heated at the timeof forming the mask.

[0015] Also, the invar mask has a low structural intensity compared to amask of AK material (AK mask) and causes a drop characteristicdeterioration, so that a wedge ratio of a panel (a ratio of a cornerthickness of a panel for a center thickness) was set to be 220% or morethan and a mask curvature was set to be similar to a spherical type,that is, to be similar to a single curvature radius R in theconventional art. According to this, an optimum curvature of a panelwhich is light, reduces a fabrication cost, and increases a structuralintensity could not be implemented.

SUMMARY OF THE INVENTION

[0016] Therefore, an object of the present invention is to provide acolor cathode ray tube capable of obtaining a structural intensity of amask corresponding to a panel, decreasing a partial doming, andincreasing a drop characteristic by setting a curvature of the panel tobe greater from a center portion of the panel towards a peripheralportion thereof.

[0017] To achieve these and other advantages and in accordance with thepurpose of the present invention, as embodied and broadly describedherein, there is provided a color cathode ray tube comprising: a panelof which an outer surface is substantially plane and an inner surfacehas a predetermined curvature; and a mask for selecting colors ofelectron beams incident from inside of the panel, in which a formula,0.3≦(Rxe/Rxc)≦0.75 is satisfied.

[0018] The foregoing and other objects, features, aspects and advantagesof the present invention will become more apparent from the followingdetailed description of the present invention when taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings, which are included to provide afurther understanding of the invention and are incorporated in andconstitute a part of this specification, illustrate embodiments of theinvention and together with the description serve to explain theprinciples of the invention.

[0020] In the drawings:

[0021]FIG. 1 is a longitudinal section view showing a color cathode raytube in accordance with the conventional art;

[0022]FIG. 2 is a longitudinal section view showing a color cathode raytube according to the present invention;

[0023]FIG. 3 is a perspective view showing an effective surface of apanel in a color cathode ray tube according to the present invention;

[0024]FIG. 4 is a graph showing a super arc ratio;

[0025]FIG. 5 is a graph showing a drop quality and B/U according to awedge ratio in a color cathode ray tube using an AK mask;

[0026]FIG. 6 is a graph showing a drop quality and B/U according to awedge ratio in a color cathode ray tube using an invar mask;

[0027]FIG. 7 is a graph showing a drop characteristic and a partialdoming according to Rxe/Rxc;

[0028]FIG. 8 is a graph showing a drop characteristic and a partialdoming according to Rye/Ryc; and

[0029]FIG. 9 is a graph showing a drop characteristic and a partialdoming according to Rye/Rxc.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Reference will now be made in detail to the preferred embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings.

[0031] Hereinafter, a color cathode ray tube according to the presentinvention will be explained in more detail.

[0032]FIG. 2 is a longitudinal section view showing a color cathode raytube according to the present invention, and FIG. 3 is a perspectiveview showing an effective surface of a panel in a color cathode ray tubeaccording to the present invention.

[0033] As shown in FIGS. 2 and 3, in the color cathode ray tube of thepresent invention, a curvature of a panel is increased from a centerportion of the panel 10 towards a peripheral portion of an effectivesurface at the time of forming an inner curvature of the panel.

[0034] In case of increasing the inner curvature of the panel from thecenter portion of the panel 10 towards the peripheral portion of theeffective surface (hereinafter, a super arc), a structural intensity ofa mask corresponding to the inner curvature of the panel can beobtained, thereby effectively solving problems such as a partial dominggenerated at the time of using an AK mask or a tint panel.

[0035] Especially, in the present invention, the partial doming can bemore effectively reduced by forming an inner curvature of the panel tobe relatively greater than a curvature of the center portion at a ⅔region from the effective surface center portion towards the peripheralportion of the panel, the weakest region for the partial doming of thecathode ray tube.

[0036] Hereinafter, a long axis is defined as a line in the center ofthe panel parallel to a longer side of the panel, a short axis isdefined as a line in the center of the panel parallel to a shorter sideof the panel, a Rxe is defined as an inner curvature radius at an edgeof a long axis of the panel, a Rye is defined as an inner curvatureradius at edge of a short axis of the panel, a Ryc is defined as aninner curvature radius at a center of a short axis of the panel, a Rxcis defined as an inner curvature radius at a center of a long axis ofthe panel, a Rdc is defined as an inner curvature radius at a center ofa diagonal axis of the panel, a Rde is defined as an inner curvatureradius at a edge of a diagonal axis of the panel, and a USD is definedas an effective surface diagonal distance of the panel.

[0037] The color cathode ray tube according to the present inventioncomprises a panel 10 of which an outer surface is substantially planeand an inner surface has a predetermined curvature, a mask 20 forselecting colors of electron beams, a funnel 30 coupled to a rearsurface of the panel 10 for maintaining inside of the cathode ray tubeas a vacuum state, an electron gun 50 for emitting electron beams, and adeflection yoke 60 for deflecting electron beams. At the time of formingthe inner curvature of the panel 10, the panel curvature is increasedtowards the peripheral portion of the effective surface from the centerportion of the panel 10, and a formula, 0.3≦(Rxe/Rxc)≦0.75 is satisfied.

[0038] Also, formulas, 4.5≦Rxc/USD≦8.5, 0.3≦Rye/Ryc≦1.0, and Rxe≦Rde≦Ryeare satisfied, and the USD is 500 mm or less than.

[0039] In the color cathode ray tube of the present invention, a mask ofAK material or a mask of invar material can be used. In case of using amask of AK material, formulas, 0.3≦(Rxe/Rxc)≦0.5, 4.5≦(Rxc/USD)≦8.5,0.3≦(Rye/Ryc)≦1.0, and Rxe≦Rde≦Rye are preferably satisfied, and the USDis 500 mm or less than. Also, a transmission ratio of the center portionof the panel 10 is 45%˜75%, and the wedge ratio is 180%˜220%.

[0040] In case of using a mask of Fe—Ni based alloy invar or a Fe—Ni—Cobased alloy ultra invar, formulas, 0.5≦(Rxe/Rxc)≦0.75,4.5≦(Rxc/USD)≦6.5, 0.3≦(Rye/Ryc)≦1.0, and Rxe≦Rde≦Rye are satisfied, theUSD is 500 mm or less than, and the wedge ratio is 200% or more than.

[0041] Hereinafter, the super arc ratio of the color cathode ray tubeaccording to the present invention will be explained.

[0042]FIG. 4 is a graph showing the super arc ratio.

[0043] a: curvature value Z of an edge of the effective surface of thepanel

[0044] (Z is height difference between a point on the inner surface ofthe center portion of the panel and a point on the inner surface of theperipheral portion of the effective surface of the panel)

[0045] b: curvature value Z at a ½ point from the center of the paneltowards the edge of the effective surface

[0046] horizontal axis: distance (mm) from the center of the panel tothe edge of the effective surface

[0047] vertical axis: curvature radius/curvature value (Z)

[0048] In the conventional color cathode ray tube, the inner curvatureradius of the panel is formed as a single R, so that the inner curvatureradius from the center portion of the panel to the edge of the effectivesurface is equal. However, in the color cathode ray tube of the presentinvention, the inner curvature radius of the panel is formed as a superarc and a mask curvature corresponding to the inner curvature of thepanel is designed as a super arc without an infection point, therebyobtaining a structural intensity of the mask, increasing a dropcharacteristic, and thus reducing a partial doming.

[0049] Also, in the color cathode ray tube of the present invention, thecurvature value(Z) is drastically increased from the center portion ofthe panel towards the peripheral portion, which shows that a curvatureis drastically increased from the center portion of the panel towardsthe peripheral portion.

[0050] Hereinafter, the AK mask and the invar mask will be explainedwith comparison each other.

[0051]FIG. 5 is a graph showing a drop quality and B/U according to awedge ratio in a color cathode ray tube using the AK mask.

[0052] As shown, a thermal expansion of the AK mask is approximately 5times greater than that of the invar mask, so that a partial doming thata color purity of a screen is deteriorated has to be solved at the timeof using the AK mask.

[0053] That is, in case of using the invar mask, the partial doming is20 μm or less than thus not to generate a phenomenon that the colorpurity of the screen is deteriorated. However, in case of using the AKmask, the partial doming is 70 μm or more than, which corresponds toapproximately 3 times of the invar mask in the same curvature mask andcauses the color purity of the screen to be deteriorated.

[0054] The mask curvature is varied according to the inner curvature ofthe panel even in case of a mask having the same wedge ratio, so thatthe inner curvature of the panel has to be designed as a form to reducethe partial doming.

[0055] In case of a cathode ray tube using the AK material mask, a dropcharacteristic and B/U according to the wedge ratio of the panel areshown in a following table 1 and FIG. 5. TABLE 1 Wedge ratio (%) 170 180190 200 210 220 Drop characteristic 25 30 35 40 45 50 B/U 80 78 76 74 7270

[0056] As shown in the table 1 and FIG. 5, a drop characteristic ofcathode ray tube for a general monitor (CDT), 30 G or more than, issatisfied in case of the panel wedge ratio of 180%˜220%. However, whenthe wedge ratio exceeds 220%, the B/U, brightness of a corner of ascreen of a monitor for a center, is lowered into 70% or less than,thereby having a difficulty in using a tint panel.

[0057] Accordingly, in order to use the AK mask and the tint panel, thewedge ratio of the panel has to be 180%˜220% and the B/U has to be 70-78thus to satisfy a required drop characteristic of the CDT.

[0058]FIG. 6 is a graph showing a drop quality and B/U according to awedge ratio in a color cathode ray tube using an invar mask.

[0059] As shown, in case of a cathode ray tube using an invar mask, thedrop characteristic and B/U according to the wedge ratio of the panelare shown in a following table 2 and FIG. 6. TABLE 2 Wedge ratio (%) 190200 210 220 230 240 Drop characteristic 28 30 32 34 36 38 B/U 93 92 9190 89 88

[0060] As shown in the table 2 and FIG. 6, in case of using the invarmask, the wedge ratio has to be 200% or more than in order to satisfythe drop characteristic and the B/U can be satisfied regardless of thewedge ratio.

[0061] A following table 3 shows a reducing ratio of the partial domingaccording to a variance of the curvature radius. TABLE 3 Curvatureradius (mm) 1600 1500 1400 1300 1200 1100 Partial doming 23 21 19 17 1514 Reducina ratio −9.5 0 9.5 19 28 33

[0062] As shown in the table 3, as a measurement result of the partialdoming with an invar mask having a thickness of 0.12 mm, when thecurvature radius of the panel is varied from 1500 mm to 1100 mm (when acurvature is increased), the is partial doming is varied from 21 μm to14 μm, which means the partial doming is varied nearly similarly to thevariation ratio of the curvature radius of the panel. That is, the table3 shows that the partial doing is decreased accordingly as the innercurvature of the panel is increased.

[0063] As can be seen from said result, in order to use the AK mask andthe tint panel, the wedge ratio of the panel has to be 180%˜220% thus tosatisfy required drop characteristic of the CDT. Also, in case of usingthe invar mask, the wedge ratio has to be 220% or more than in order tosatisfy the drop characteristic.

[0064]FIG. 7 is a graph showing a drop characteristic and a partialdoming according to Rxe/Rxc.

[0065] As shown, the super arc ratio of the inner curvature of the panelalong a long axis has to exceed 20% in order to satisfy 30 G(Gravity),the drop characteristic of the cathode ray tube in a wedge ratio of 220%or less than even if a structural intensity of the mask is increased byusing the AK material.

[0066] In order to decrease the partial doming with 30% or more than,the super arc ratio has to be increased. In this case, a ratio of theinner curvature radius of the effective surface edge for the innercurvature radius of the center portion of the panel along the long axissatisfies a following formula, 0.3≦(Rxe/Rxc)≦0.75, more preferably,formulas, 0.3≦(Rxe/Rxc)≦0.5, 4.5≦(Rxc/USD)≦8.5, 0.3≦(Rye/Ryc)≦1.0, andRxe≦Rde≦Rye. Also, the USD, a diagonal size of an effective surface ofthe panel is 500 mm or less than, a transmission ratio of the centerportion of the panel is 45%˜75%, and the wedge ratio of 180%˜220% issatisfied.

[0067] Also, in case of using the invar mask and increasing the wedgeratio as 200% or more than, the super arc ratio is 22%˜24% and the innercurvature radius satisfies following formulas, 0.3≦(Rxe/Rxc)≦0.75, morepreferably, formulas, 0.5≦(Rxe/Rxc)≦0.75 and 4.5≦(Rxc/USD)≦6.5.

[0068]FIG. 8 is a graph showing a drop characteristic and a partialdoming according to Rye/Ryc.

[0069] As shown, a super arc ratio along a short axis can be expressedas 0.3≦(Rye/Ryc)≦1.0 as a relation formula of the curvature radius.

[0070] When the Rye/Ryc is 0.3 or more than, the drop characteristic ofthe cathode ray tube is satisfied. The Rye/Ryc shows a maximum value at0.45 and is gradually decreased. In case that the Rye/Ryc is 1.0 or morethan, the drop characteristic of the cathode ray tube is scarcelysatisfied.

[0071] For reference, a measuring point of the partial doming ispositioned on the longer side, so that the partial doming is influencedonly by the long axis not by the short axis. On the contrary, the dropcharacteristic is influenced by both the long axis and the short axis.

[0072]FIG. 9 is a graph showing a drop characteristic and a partialdoming according to Rye/Rxc.

[0073] As shown, the drop characteristic is satisfied even in the invarmask when the wedge ratio is 230% or more than. Therefore, in case ofapplying mask of material having a high intensity, ultra invar mask, orsuper invar mask besides the currently used invar mask, a structuralintensity of the mask is increased thus to satisfy a formula,0.3≦(Rxe/Rxc)≦0.75 in the wedge ratio of 210% or less than.

[0074] Also, in case of using a mask of another material having a middlethermal expansion coefficient between the invar material and the AKmaterial, the partial doming is decreased thus to satisfy a formula,0.3≦(Rxe/Rxc)≦0.75.

[0075] In the method for reducing the partial doming by the super arc,the Rxe, the inner curvature radius at an edge of the long axis is thesmallest and the Rye, the inner curvature radius at an edge of the shortaxis is the greatest, which can be expressed as Rxe≦Rde≦Rye.

[0076] In the present invention, the super arc ratio is graduallyincreased towards the long axis in order to form a curvature at a ⅓point of the long axis, a measuring point of the partial doming greatly.Therefore, the inner curvature of the edge of the effective surfacealong the long axis is relatively formed to be greater than that alongthe short axis or that along the diagonal axis.

[0077] The present invention is more effective in a cathode ray tube of21″ or less than of which USD is 500 mm or less than. Also, in case of alarge cathode ray tube, since the large cathode ray tube requires lowerdrop characteristic G than a smaller cathode ray tube, the presentinvention can be also applied to the large cathode ray tube.

[0078] As aforementioned, at the time of forming the inner curvature ofthe panel according to the present invention, relations among the innercurvature radius at a center of a long axis of the panel (Rxc), theinner curvature radius at an edge of a long axis of the panel (Rxe), theinner curvature radius at a center of a short axis of the panel (Ryc),the inner curvature radius at an edge of a short axis of the panel(Rye), the inner curvature radius at an edge of the diagonal axis of thepanel (Rde), and the diagonal size of an effective surface of the panel(USD) are set, and the inner curvature of the panel is increased fromthe center portion of the panel towards the peripheral portion of theeffective surface, thereby obtaining a structural intensity of the mask,thus increasing the drop characteristic, and effectively preventing thepartial doming.

[0079] As the present invention may be embodied in several forms withoutdeparting from the spirit or essential characteristics thereof, itshould also be understood that the above-described embodiments are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsspirit and scope as defined in the appended claims, and therefore allchanges and modifications that fall within the metes and bounds of theclaims, or equivalence of such metes and bounds are therefore intendedto be embraced by the appended claims.

What is claimed is:
 1. A color cathode ray tube comprising: a panel ofwhich an outer surface is substantially plane and an inner surface has apredetermined curvature; and a mask for selecting colors of electronbeams incident from inside of the panel, in which a formula,0.3≦(Rxe/Rxc)≦0.75 is satisfied, wherein the Rxe is an inner curvatureradius at an edge of a long axis of the panel, and the Rxc is an innercurvature radius at a center of a long axis of the panel.
 2. The colorcathode ray tube of claim 1, wherein the inner curvature radius isgradually decreased from a center portion of the panel towards aperipheral portion of the panel.
 3. The color cathode ray tube of claim1, wherein the mask is formed of AK material.
 4. The color cathode raytube of claim 1, wherein a formula, 4.5≦(Rxc/USD)≦8.5 is satisfied,wherein the USD is a diagonal size of an effective surface of the panel.5. The color cathode ray tube of claim 3, wherein a formula,0.3≦(Rxe/Rxc)≦0.5 is satisfied.
 6. The color cathode ray tube of claim1, wherein a USD of the panel is 500 mm or less than, wherein the USD isa diagonal size of an effective surface of the panel.
 7. The colorcathode ray tube of claim 1, wherein a transmission ratio of a centerportion of the panel is 45%˜75%.
 8. The color cathode ray tube of claim1, wherein an wedge ratio is 180%˜220%.
 9. The color cathode ray tube ofclaim 1, wherein the mask is formed of either Fe—Ni based alloy orFe—Ni—Co based alloy.
 10. The color cathode ray tube of claim 9, whereina formula, 0.5≦(Rxe/Rxc)≦0.75 is satisfied.
 11. The color cathode raytube of claim 9, wherein a formula, 4.5≦(Rxc/USD)≦6.5 is satisfied,wherein the USD is a diagonal size of an effective surface of the panel.12. The color cathode ray tube of claim 9, wherein a USD of the panel is500 mm or less than, wherein the USD is a diagonal size of an effectivesurface of the panel.
 13. The color cathode ray tube of claim 9, whereinan wedge ratio is 200% or more than.
 14. The color cathode ray tube ofclaim 1, wherein a formula, Rxe≦Rde≦Rye is satisfied, wherein the Rxe isan inner curvature radius at an edge of a long axis of the panel, theRye is an inner curvature radius at an edge of a short axis of thepanel, and the Rde is an inner curvature radius at an edge of a diagonalaxis of the panel.
 15. The color cathode ray tube of claim 2, wherein aformula, Rxe≦Rde≦Rye is satisfied, wherein the Rxe is an inner curvatureradius at an edge of a long axis of the panel, the Rye is an innercurvature radius at an edge of a short axis of the panel, and the Rde isan inner curvature radius at an edge of a diagonal axis of the panel.16. The color cathode ray tube of claim 7, wherein a formula,Rxe≦Rde≦Rye is satisfied, wherein the Rxe is an inner curvature radiusat an edge of a long axis of the panel, and the Rde is an innercurvature radius at an edge of a diagonal axis of the panel.
 17. Thecolor cathode ray tube of claim 1, wherein a formula, 0.3≦(Rye/Ryc)≦0.5is satisfied, wherein the Rye is an inner curvature radius at a centerof a short axis of the panel, and the Ryc is an inner curvature radiusat a center of a short axis of the panel.